On demand geometry and acceleration structure creation

ABSTRACT

Systems and methods of geometry processing, for rasterization and ray tracing processes provide for pre-processing of source geometry, such as by tessellating or other procedural modification of source geometry, to produce final geometry on which a rendering will be based. An acceleration structure (or portion thereof) for use during ray tracing is defined based on the final geometry. Only coarse-grained elements of the acceleration structure may be produced or retained, and a fine-grained structure within a particular coarse-grained element may be produced in response to a collection of rays being ready for traversal within the coarse-grained element. Final geometry can be recreated in response to demand from a rasterization engine, and from ray intersection units that require such geometry for intersection testing with primitives. Geometry at different resolutions can be generated to respond to demands from different rendering components.

BACKGROUND Field

In one aspect, the following relates to rendering systems that usegeometry inputs defined in 3-D space.

Related Art

Rendering of images (as an example rendering output) from a 3-D scenedescription can be accomplished using a variety of approaches. Oneapproach uses rasterization techniques, in which primitives are mappedfrom 3-D coordinates to a 2-D screen space, in order to determine avisible surface, which can then be textured and shaded. Another approachis to use ray tracing, which involves tracing rays through the 3-Dspace. Ray tracing can better model effects reflections and refractions,and can generate highly complex and physically accurate images.

Both rasterization and ray tracing use geometry data as an input, todefine objects that are located in the 3-D scene. Geometry data definethe extent of surfaces in the scene, but not their ultimate coloration,and texture, for example. However, detailed geometry can yield importantadvances to realistic and enjoyable computer graphics experiences. Therecan be a tradeoff between detail in an object and an amount of memoryrequired to store the geometry data representing the object.

SUMMARY

One aspect relates to a machine-implemented method for use in 3-Drendering. The method comprises accessing geometry data describinggeometry located in a 3-D scene, from which a rendering is to beproduced, the data describing geometry control points and proceduralmodifications that can be performed on the geometry control points toproduce final geometry on which the rendering will be based. The methodalso comprises producing, using the final geometry, geometry extentsdata that each establish an association between a volume defined in the3-D scene and a selection of the geometry control points that, afterprocedural modification, if any, produce final geometry thatrespectively is within that volume.

Such a method may further comprise defining rays to be traced in the 3-Dscene, by identifying a volume in the 3-D space in which a subset of therays is to be tested for intersection and using the geometry extentsdata to identify geometry control points that produce final geometry inthe identified volume in the 3-D space. Then, the method furthercomprises executing any procedural modifications for those identifiedgeometry control points to produce final geometry in the identifiedvolume, and then testing final geometry for intersection with the subsetof the rays.

The method may further comprise producing an acceleration structurecomprising elements bounding respective portions of the 3-D scene, andusing the acceleration structure to identify respective subsets of thefinal geometry to be tested for intersection with different rays. Themethod may further comprise using hint data to define the volumes in the3-D scene that are referenced in the geometry extent data. The methodmay further comprise associating procedural modifications with geometryextents data that are required to produce final geometry within a volumeof the 3-D scene to which the geometry extents data pertains.

The method also may further comprise making a rendering using both arasterization subsystem and a ray tracing subsystem that each makerequests for portions of final geometry, and responsive to the requests,producing the final geometry by performing the procedural modificationsassociated with the geometry extents data associated with volumes of the3-D scene bounding the requested portions of final geometry.

The method also may further comprise producing final geometry having alevel of detail dependent on whether to the request originated from theray tracing subsystem or the rasterization subsystem.

The method also may further comprise producing both a finalizedacceleration structure within a portion of the 3-D scene and finalgeometry within that portion of the 3-D, responsive to a request fromthe the ray tracing subsystem.

The method also may further comprise producing a coarse accelerationstructure with leaf elements and using leaf elements of the coarseacceleration structure as the geometry extents data.

The method also may further comprise collecting rays to be tracedagainst elements of the coarse acceleration structure and traversingrays collected against a particular element of the coarse accelerationstructure by dynamically producing a finalized acceleration structurewithin that particular element of the coarse acceleration structureprior to scheduling traversal operations for the collected rays.

The method also may further comprise producing final geometry withinportions of the finalized acceleration structure responsive to ascheduler indication.

The method also may further comprise performing the accessing andproducing in a pre-pass over source geometry data, the source geometrydata comprising vertex data and two or more sets of vertex connectivitydata.

The procedural modifications that can be performed on the geometrycontrol points may comprise procedural modifications to be used forproducing finalized geometry for ray tracing and proceduralmodifications to be used for producing finalized geometry forrasterization.

Aspects also may provide for the producing of the geometry extents datato comprise producing a hint indicating an amount of geometry expansionto be expected when producing final geometry for the volume defined inthe 3-D scene that is associated with that portion of geometry extentsdata.

Methods may implement the accessing by accessing a hint that isassociated with a control point, which indicates a bound on an amount ofgeometry that may result when performing procedural modification usingthat control point, to produce final geometry.

Another aspect provides a method of geometry processing for 3-Drendering. The method comprises producing geometric primitives locatedin a 3-D scene from source geometry data and defining a set of tileobject lists. Each tile object tile contains data indicating whichsource geometry from the set of source geometry results in geometricprimitives that are within a boundary of a respective tile of pixels ofa 2-D image. The method also comprises producing an accelerationstructure comprising a graph of elements, each defining a respectivevolume in the 3-D scene and rendering the 2-D image from the scene byusing the tile object lists to identify a visible surface at each pixelof the 2-D image, and tracing rays in the 3-D scene, using theacceleration structure, from the identified visible surfaces to identifya primitive intersected by each of the rays, if any, and producinginformation contributing to a final shade for the visible surface ateach pixel.

Another aspect provides a method of 3-D geometry processing for graphicsrendering. The method comprises defining a respective set ofmodification processes to be performed on portions of source geometry,in order to produce final geometry located in respective portions of a3-D scene and producing a respective element of an accelerationstructure that bounds each of the portions of the 3-D scene andassociating, with the element. The respective set of modificationprocesses are performed in order to produce final within that element.The method also comprises defining a set of tile object lists. Each tileobject list identifies source geometry and a respective set ofmodification processes to be performed on the identified source geometryto produce final geometry within a tile of pixels within a 2-D image tobe rendered from the 3-D scene, and rendering the 2-D image byidentifying visible surfaces for pixels within the 2-D image on a tileby tile basis. The rendering comprises identifying source geometry fromthe tile object list for each tile, and performing the set ofmodification processes on the source geometry to produce final geometry.A visible surface for each pixel in that tile is identified based on theproduced final geometry, and to complete the rendering for a group ofthe pixels, rays are emitted from the visible surface for pixels andtraversed in the 3-D scene. The rays are traversed in the 3-D scene.

Another aspect provides a method of 3-D geometry processing for graphicsrendering. The method comprises producing final geometry from sourcegeometry by applying one or more geometry modification processes to thesource geometry, the production of the final geometry limited to asubset of final geometry located in a 3-D scene from which a 2-Drendering is being made; and controlling caching of particular portionsof the produced final geometry, based on demand indicated for theparticular portions of the produced final geometry by one or moreconsumers thereof.

Another aspect provides a method of 3-D geometry processing for graphicsrendering, comprising producing final geometry from source geometry byapplying one or more geometry modification processes to the sourcegeometry, the producing characterized by a plurality of discreteproductions, each producing final geometry limited to a subset of finalgeometry located in a 3-D scene; and scheduling the plurality ofdiscrete productions of the final geometry by collecting requests forparticular sub-sets of final geometry into groups and based on ascheduling criteria, and relatively ordering the plurality of discreteproductions according to the scheduling criteria.

A further aspect provides a method of 3-D geometry processing forgraphics rendering, comprising producing final geometry from sourcegeometry by applying one or more geometry modification processes to thesource geometry, the producing characterized by a plurality of discreteproductions, each producing final geometry limited to a subset of finalgeometry located in a 3-D scene; and scheduling the plurality ofdiscrete productions of the final geometry by collecting requests forparticular sub-sets of final geometry into groups and based on ascheduling criteria, and relatively ordering the plurality of discreteproductions according to the scheduling criteria.

Any of these aspects may be implemented in a computing system. Such acomputing system may comprise programmable elements that can beprogrammed to implement geometry modification processes, controlprocesses, shading processing, including shading processes for shadingvisible surfaces determined from rasterization and also shading rayintersections. The computing system may comprise fixed or limitedfunction elements, such as fixed or limited function elements for raytracing operations, such as traversing rays through an accelerationstructure or testing rays for intersection with geometric primitives.Systems implementing aspects of the disclosure may comprise bothrasterization and ray tracing subsystems. These different subsystems maybe implemented on common hardware, with different software. Othersupporting hardware may be provided in such systems, including texturingsampling and blending. Such systems may comprise one or more memoriesfor storing source geometry, and cache(s) for storing finalizedgeometry. These memories may be part of a memory hierarchy. Such systemsmay be part of a portable device, such as a tablet or smartphone, alaptop or desktop computer, or embedded, such as embedded within adevice, such as a television or appliance.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts components of an example system for on demand geometryprocessing;

FIGS. 2A-C depict aspects of an example process for on-demand geometryin a system that performs both rasterization and ray tracing;

FIG. 3 depicts an example implementation by which source geometry datacan be submitted through an API, and the source geometry data caninclude hints that indicate or which can be used to derive volumetricbounds of final geometry that will result from a particular set orelement of source geometry data.

FIG. 4 depicts a view frustrum and a tile located therein;

FIGS. 5-6 depicts an example of a Bezier patch surface that has a shelldefined by planar patches;

FIG. 7 depicts an example process of defining an acceleration structurebased on information relating to tessellated geometry, such as tuning alevel of coarseness in an acceleration structure that will be used tosubdivide a 3-D scene into different portions, for the purpose ofon-demand creation of final geometry of those different portions;

FIG. 8 depicts an example process of multi-resolution on geometrygeneration;

FIG. 9 depicts storage of source geometry data for multi-resolutiongeometry generation;

FIG. 10 depicts an example process of scheduling geometry and/oracceleration structure creation tasks;

FIG. 11 depicts an example of data that can be used in schedulinggeometry and/or acceleration structure creation tasks;

FIG. 12 depicts an example of data representing ray traversal status;

FIG. 13 depicts an example modular structure of function elements;

FIG. 14 depicts an example block diagram of system elements that can beused to implement the functional elements of FIG. 13;

FIG. 15 depicts an example of a vectorized execution unit that can bepart of the system elements of FIG. 14.

DETAILED DESCRIPTION

Techniques to reduce an amount of memory required to represent adefinition of the surface of an object include specifying surfaces ofobjects as patches that have control points, which can be used toproduce vertexes of primitives. Additionally, vertexes of primitives canbe used as input to tessellation and to geometry shaders or displacementengines that can amplify a number of primitives by dicing a largerprimitive into smaller ones, or otherwise deform geometry so that anextent of geometry after these further geometry operations is differentfrom an original extent.

In an unconstrained memory resource environment, it may be acceptable tosimply produce final geometry for an entire 3-D scene, and store it in afast Random Access Memory. However, in a computing environment in whichfast memory resources are constrained, it may be impossible orundesirable to allocate enough memory to store such data.

The following relates to approaches for reducing a memory footprintrequired to store geometry, in order to render images of a givencomplexity. Aspects disclosed below relate both to rasterization and raytracing approaches to rendering. Such approaches also can be adapted toother situations in which complex 3-D geometry may need to be used in amemory constrained environment. Memory constrained does not imply anyspecific memory constraint, but rather is related to the complexity ofgeometry sought to be used. As such, a memory constraint is a designconsideration in an overall platform. If memory footprint to processgeometry of a given complexity can be reduced, then a bill of materialsfor a device may be reduced by including less memory.

In one aspect, an implementation of the disclosure performs a pre-passthat gathers information, generates information, or both gathers andgenerates information that defines how a set of input geometry dataresults in a set of geometry data that is used in scene rendering. Forexample, in one approach, the source scene geometry can be run through ageometry pipeline, which can include translating patches into a set ofprimitives, tessellating these primitives into other primitives,performing displacement mapping, and running geometry shaders on thisdata. This pre-pass can be performed before rendering of the scenebegins, or can be performed for the first time that a given scene isused for rendering.

An output of this pre-pass is a description of where the final geometryexists. This description can be varied according to what type or typesof rendering is to be performed. For example, in the context of atile-based rendering system, such information can include a descriptionof which original elements of geometry ultimately produce a primitive orother portion of geometry that is within the bounds of each screen-spacetile. In the context of ray tracing, such information can include a setof bounding boxes, or a coarse acceleration structure that identifiesbounding volumes that will function as geometry expansion points in 3-Dspace. There can be an association between each original primitive andeach bounding volume that contains a part of final geometry resultingfrom that original primitive. A variety of more specific examples areprovided below.

A wide variety of approaches to specifying 3-D scene geometry areavailable. For simplicity, the disclosure provides examples ofimplementations that begin with a surface patch, which can be used todefine vertexes, that can be amplified by tessellation or displaced, oroperated on by programmable geometry shading are disclosed.Additionally, an approach to on-demand geometry in the context of TileBased Deferred Rendering (TBDR) is disclosed, in addition to an approachfor ray tracing rendering.

First, the plurality of primitives are tessellated primitives generatedby tessellating a patch of surface data. However, it will be appreciatedthat implementations are not limited to this embodiment and may be usedequally with tessellated primitives generated by other means or withnon-tessellated primitives.

Geometry Processing

FIG. 1 shows a schematic diagram illustrating a graphics pipeline forgenerating and shading a computer graphics image in a tile-basedrendering system that supports both tessellation and ray tracing oftessellated geometry.

Geometry data 25 defines objects in 3-D space for use during rendering.Geometry data 25 may include descriptions of higher order surfaces, suchas patches (e.g., Bezier patches), meshes of primitives defined byvertexes and connectivity data, or other ways to specify geometry.Geometry data 25 is supplied to a geometric processing unit 61 which canmanipulate geometry data, and can derive primitives from the objectdata, or otherwise produce a specification of geometry that can be usedfor the geometry processing to be performed. Geometry data 25 can be inone or more formats as submitted through an Application ProgrammingInterface (API) during a rendering setup process. For example, if boththe ray tracing and the rasterization processes to be performed by therendering system consume triangular primitives, then geometry processingunit 61 can input higher order surface descriptions and output a mesh oftriangular primitives.

In an example, geometry data 25 can be submitted (e.g. streamed) forprocessing. In an example, patches of geometry can be supplied to avertex shader 27, which can in turn provide shaded vertex data to a hullshader 29. Vertex shader 27 can, for example, programmatically movecontrol points of patches (e.g., a combination of one or more oftranslation, rotation, or scaling), or perform initial vertex lighting,or both, or other types of programmatic operations on these controlpoints. These control points can be provided to units that performtessellation-related functions.

Tessellation involves breaking up a low detail model, for example ahigher order surface, which can be referred to as a “patch”, into aplurality of tessellated primitives. A “patch” is typically a functionof a polynomial equation which defines a set of control points whichdescribe the shape of a curve with respect to variable ‘t’ (for a curvein two dimensions) or domain coordinates ‘u,v’ (for a curve in threedimensions). One example of a patch used in computer graphics is aBezier patch, but others exist as will be appreciated by a personskilled in the art. At present, flat patches are commonly used, forexample triangular patches, which are split into multiple primitiveswhich are then displaced by a function and/or in dependence on adisplacement height map to create a plurality of tessellated primitives.Tessellation is an example of an approach to programmatically deriving aplurality of primitives from a description of a surface. A patch is asurface defined by a parametric relationship (e.g., for 3-D, uvcoordinates). Points on the surface can be defined using the parametriccoordinates. As will be known to those skilled in the art, tessellationof patches of surface data in a graphics pipeline can be supported by anumber of application programming interfaces (API's), for example,Microsoft's Direct 3D11 API. Microsoft's Direct 3D11 API supportsdisplacement mapping, whereby the tessellated primitives may be at adisplaced location from the surface of the patch.

Programmable vertex shading, as can be applied to patches or toindividual primitives, can be used to generate modified primitivesaccording to a functional description. For example, where programmablevertex shading is employed at vertex shading 27, the outputs of thatvertex shading can be tessellated. As an example, a plurality ofmodified primitives or patches can be generated from input geometry,where each of the modified primitives or patches is at a displacedlocation from a location of source geometry from which it was derived.Each of these modified elements of geometry may be generatedincrementally. For example, a first generated primitive may be closestto a position of the original primitive, and each of thesubsequently-generated primitives may be progressively farther from theposition of the input primitive. Another example is a defocus blurapplication, where a plurality of modified primitives may be generatedat small offsets from an input primitive, without necessarily being atincreasing distances from the input primitive. However, in general,modified primitives may be generated in any order or sequence, includingan arbitrary order.

Hull shader 29 can calculate tessellation factors for edges of a givenpatch and may also further modify the transformed control points. Hullshader 29 outputs to domain tessellation 31 and connectivitytessellation 33. Domain tessellation subdivides a patch into a number ofknown points called “domain” points based on the tessellation factors.Connectivity tessellation 33 determines how the domain points arecombined or connected to produce tessellated primitives. Thesefunctional modules may operate in accordance with a standardizedtessellation approach, such as DX11. These domain points are passed to adomain shader 35 which uses this data, along with control pointsproduced by the hull shader according to a programmable geometry shader37. Shader 37 can perform further programmable shading operations ongeometry and produce vertices to be stored in vertex cache 41. Verticesstored in vertex cache 41 can serve as a basis for producing data to beused during rasterization (e.g., tile-based rasterization) and duringray tracing operations.

Regarding preparations to perform tile-based rasterization, as shown inFIG. 1, the vertices from vertex cache 41 are provided to a clip/cullunit 43 that removes geometry that is not within a scope of visibilityfor a 2-D image being rendered (e.g., it is off screen or back-facing).Remaining geometry is projected to a 2-D coordinate system for the 2-Dimage by projection unit 45.

The projected geometry is tiled by a tiling unit 47 (a tile is a regionof pixels, such as a rectangular region of pixels). Tiling unit outputsinformation that identifies which geometry is at least partially withinthe bounds of each tile. This information can take the form of anidentifier for a tile and a list of geometry that is at least partiallywithin that tile. In the context of the present disclosure, the geometrybeing tiled may include tessellated geometry. As explained above,tessellated geometry is geometry that was derived from source geometry.In the context of the present disclosure, the information identifying atile and a list of geometry can include identifying information forsource geometry; this information may be called an “object list” for aparticular tile. Object lists may be stored in memory, for example in abuffer. To rasterize and shade each tile for display, an object list forthat tile can read.

In complex 3-D rendering, a voluminous amount of data may be generatedor required in order to individually identify each primitive. Therefore,in some implementations, an approach to compressing this data may beemployed. When the data for a tile is to be used, then a reversecompression or other interpretation can be applied to the data containedin the object list for that tile.

In FIG. 1, a processing element that produces bounding volumes 39 canoperate on final geometry within sub-volumes of 3-D space using verticesproduced as a result of programmable geometry shading 37, which verticescan be stored in vertex cache 41. That geometry extents data can bestored in non-transitory memory 57. During 3-D operations, such as raytraversal or ray intersection testing, a portion of final geometry maybe (re)created and stored in non-transitory memory 55. Non-transitory 55may be implemented in a variety of ways and FIG. 1 does not imply thatnon-transitory memory 55 is a single physical memory. A geometry unitcontroller 61 can operate to indicate which portions of geometry are tobe processed (e.g., scheduling production or supply of final geometry toconsumers thereof, as explained below).

Rasterization 54 can use an output of a screen space geometry buffer 51,which expresses final geometry mapped to screen space. For example,rasterization 54 can operate on tiles of geometry. An output ofrasterization 54 includes visible surfaces, which may be submitted topixel shading 51, which outputs pixel shade results data to an outputbuffer 72. In general, such pixel shading may be included within atexturing and shading unit 52, which may be implemented on aprogrammable computation unit or cluster of units. This unit 52 also mayimplement ray shaders 53. Ray shaders 63 may be triggered based onoutputs of ray tracing unit(s) 59. Ray tracing units may identifyclosest intersections between final geometry and rays. Theseintersections may be shaded according to programmable shading modules.Ray tracing units 59 may use ray data 65 during ray traversal. Rayshaders 63 also may access such ray data 65, and may store new rays inray data 65.

Compressed Tile Object Lists

Tiling unit 47 divides an image into a plurality of tiles, eachcomprising a plurality of image pixels. Tiles are typically rectangularbut can be other shapes. For each tile, tiling unit 47 determineswhether each of the primitives is located at least partially within thattile. That is, tiling unit 47 determines whether at least part of thatprimitive is located within a viewable region of the tile. Tiling unit47 also derives an object list for each tile. The object list indicatesprimitives located at least partially within that tile. An object listcan be created for each tile, even if there are no primitives locatedwithin a tile, and in such case, the object list for that tile is empty.In some implementations, not every primitive determined to be locatedwithin a tile is actually indicated in the object list for that tile.For example, it may be determined, at the tiling stage, that a primitiveis obscured by other primitives in the tile (e.g., a step of hiddensurface removal can be employed during tiling), and therefore will notbe visible within the tile. That primitive may therefore not beindicated in the object list for that tile, to save processing thatprimitive unnecessarily later.

The primitives may be indicated in a number of ways. Identifiersidentifying each of the primitives can be stored in respective objectlists. Each primitive may, for example, be assigned an index, or each ofthe vertices of the primitives may be assigned an index. Theseidentifiers may reference or provide a pointer to the geometrical datafor the respective primitives or primitive vertices. Another example isthat, for each tessellated primitive, rather than storing the fullgeometrical data for the primitive, data is stored from which a finalgeometry can be derived. For example, a set of control points for thepatch and the tessellation parameters, from which the geometrical datafor that primitive can subsequently be derived.

As another example, modified primitives (e.g., primitives resulting fromtessellation or other geometry shading) can be indicated in objectlists. For example, each of the modified primitives can be assigned aunique identifier. For example, each of the modified primitives may beassigned a consecutive integer. If the input primitive is assigned theinteger 0, the plurality of new instances of the primitive (orprimitives resulting from processing that input primitive) mayrespectively be assigned the integers 1, 2, 3, 4 . . . n. If it isdetermined that one or more of the modified primitives is located atleast partially within a tile, then the unique identifier for each ofthose modified primitives is stored in the object list for that tile.

An alternative method for indicating modified primitives may proceed asfollows. If it is determined that one or more of the modified primitivesis located within a tile, an identifier (the index/indices) for theinput primitive, from which those modified primitives are generated, isstored in an object list for that tile. In other words, each of themodified primitives may be assigned the same identifier (index/indices)as the input primitive. For example, if the input primitive is assignedthe integer 0, then each of the modified instances of that primitive arealso assigned the index 0. The index/indices for the input primitive maybe stored once for each of the modified instances of that primitivelocated within the tile. However, the index/indices for the inputprimitive may be stored only once per list, regardless of the number ofinstances of that primitive which are located within a particular tile.

As such, one may not be able to identify, from the object list for atile, which or how many instances of a primitive identified in theobject list are located within that tile. However, this embodimentnonetheless has the advantage that the input primitive, from which themodified instances are derived, is identified in the object list, if atleast one of the instances of that primitive is located within the tile,regardless of whether the input primitive itself is located within thattile. Thus, all modified primitives which are located within the tilemay be processed to shade the tile accurately using its object list.Furthermore, this approach enables the data stored in the object list tobe stored in a highly compressed format.

As described in more detail below, to shade the tile the same modifyingfunction is re-applied to each primitive identified in the object list.Then, once the modified primitives have been re-generated which ones, ifany, are located within the tile can be determined using well knowntechniques as described above.

This approach does have the disadvantage however that, not only must anymodified primitives located within the tile be re-generated, butmodified primitives which are not, in fact, located within the tile maybe computed unnecessarily. Given that each primitive may have hundredsor thousands of modified instances, this situation can result insignificant waste of computational resources. Therefore, in oneapproach, a flag comprising a number of bits, may be stored in theobject list for a tile or in another region of memory, indicating whichprimitives identified in the object list have a modified instance withinthe tile. This may avoid having to re-apply the modifying function toall of the primitives identified in the object list, while retaining theadvantage of being able to store the data in the object lists in ahighly compressed format.

As mentioned above, modified primitives may be generated incrementally,such that one modified primitive is created from the input primitive,and then a second modified primitive is created from that modifiedprimitive and so on until a sequence of modified primitives has beenderived. As such, in addition to storing an identifier identifying theprimitive from which the sequence of modified primitives is derived,data indicating the first and/or last position in the sequence of thosemodified primitives located within the tile may be stored. This data maybe stored in the object list for that tile or in another region ofmemory. This approach has the advantage that, where only a subset of thesequence of modified primitives is located within a particular tile, notall of the sequence of modified primitives may need to be re-derived inrespect of that tile, as will be explained in more detail below.

There is, however, the trade-off that data indicating the first and orlast sequence position needs to be stored for each of the primitivesidentified in the object list. In this described embodiment, where theprimitives are tessellated primitives, it will be appreciated by thoseskilled in the art, that there may be thousands of primitives generatedby each patch. Storing this position data for each of the primitiveswould require a large amount of memory.

A compromise may be to determine the highest and or lowest sequenceposition of any modified primitives located within the tile which arederived from tessellated primitives derived from a patch of surfacedata. This approach provides that only two integers need to be storedper tile for the entire patch. This technique may result in moreunrequired modified primitives being generated, but requires less memorywhilst avoiding re-deriving some unrequired modified primitives.

In some embodiments, there may be more than one step of shading(modifying) applied to any given element of source geometry, in order toderive final geometry. Each of these steps may apply a differentmodifying function or procedure to an input primitive. Each modifyingfunction may be assigned an identifier that identifies a modifyingfunction (or sequence thereof) to be used to generate modifiedprimitives. That identifier may be stored in an object list pertainingto a tile containing those modifying primitives. Data indicating a firstand/or last position in a sequence of the modified primitives may bestored in respect of each of the modifying units. The list of indicesmay be compressed, for example using an index/vertex buffer in a mannerknown to those skilled in the art. A number of different techniques forcompressing a list of indices of tessellated primitives derived bytessellation of a patch of surface data, which take advantage ofknowledge of the internal structure of a tessellated patch of surfacedata, may be provided. An advantage of assigning the modified primitivesthe same index/indices as the input primitive is that the samecompression techniques may be utilized to compress the index/indices.

Pre-Processing of Geometry for Ray Tracing

Processing required to prepare for ray tracing differs in some respectsfrom processing of geometry for rasterization. One principal differenceis that efficiency in ray tracing complex scenes typically is enhancedby creating an acceleration structure that has different levels ofabstraction of geometry in the 3-D scene. For example, an accelerationstructure may be a hierarchical arrangement of elements, where each ofthe elements bounds a respective volume in 3-D space. Each volume maybound a primitive, multiple primitives, or a portion thereof. Anacceleration structure for ray tracing may be created for final geometry(i.e., after programmatic geometry modification or creation, such as byusing displacement geometry or tessellation). In some cases, efficiencyof determining intersections in the 3-D scene may be enhanced byproviding a more detailed acceleration structure. However, a moredetailed acceleration structure would be expected to consume more memorythan a more granular acceleration structure.

In order to implement memory conscious rendering approaches, which useone or more of rasterization and ray tracing, techniques may be employedto avoid creating and storing final geometry for an entire 3-D scene.These techniques may involve creation of final geometry or othergeometry-related constructs (e.g., a portion of an accelerationstructure) in response to a need. After production of per-tile objectlists, tiling may proceed by stepping through each tile, and processingthe geometry indicated from each object list. Thus, depending onimplementation, tiling computation can be relatively regular andpredictable.

However, traversing rays in a 3-D scene can be very irregular,especially global illumination rays, such as reflection or refractionrays, since rays will be scattered, originating from disparate locationsand traveling in various directions (compared with primary rays tracedfrom a scene “camera”). Also, in some situations, rays may be emittedfor traversal during the tiling process, in which visible surfaces ofgeometry for pixels are determined. After these visible surfaces aredetermined, then those surfaces can be shaded, or otherwise processed.For example, rays may be cast from the surface to determine shadowing ofthat surface point by lights. Rays may stochastically emitted for globalillumination sampling for example. Herein, the term pixel is often used,but pixels may be composed of a variety of fragments. Also, multiplesamples may be taken for each pixel by offsetting the pixel in one ormore directions when determining visible surfaces for that pixel.

The pre-processing of geometry for ray tracing can benefit frompre-processing performed for tiling purposes. Pre-processing for tilingalso can benefit from geometry processing performed to setup for raytracing. Example opportunities to make pre-processing of final geometryfor tiling and for ray tracing, as well as for on-demand generation offinal geometry for tiling and ray tracing are explained.

In one aspect, geometry pre-processing for ray tracing provides forallocating final geometry among elements of an acceleration structure.The allocation of these elements in an acceleration structure can berepresented by compressed object list data for each of these elements,according to implementations of object list data, but where a decisioncriteria of whether to include the data in an object list or not iswhether the object is within a 3-D volume associated with a particularelement.

Production of Final Geometry

Final geometry produced according to the disclosure may be produced fromsource geometry which is modified according to one or more modificationfunctions. These modification functions may be applied serially. Aconcatenation of modification functions may also be expressed orcollapsed into a fewer separately identification steps or portions ofprocesses. In the context of implementations of the disclosure, wheresource geometry that produces final geometry for a particular tile orregion of 3-D space is identified in a list, that this also may containdata that identifies what geometry modification processes would beperformed on that data to result in final geometry. As such, re-creationof final geometry for particular portions of a 3-D scene (either byvirtue of being identified as relevant to a tile of screen space pixelsor a volume of 3-D space for ray tracing) may be performed by applyingthe identified sequence of modifications to the identified sourcegeometry.

The implementation of this geometry processing may be performeddifferently in different implementations. For example, where aprogrammable cluster of computation units is available to performgeometry computation, shading computation (e.g., shading of rayintersections, vertex shading, pixel shading, and so on), ray traversal,or other kinds of tasks, that programmable cluster can be configured toimplement the geometry processing required. The implementation can runthreads of computation that receive inputs and/or produce outputs fromanother thread in order to implement a sequence of geometrymodifications required. In other examples, intermediately processedgeometry data may be stored in memory and read/written as required byone or more threads of computation implementing the geometry processing.

As mentioned above, some geometry modifications may be incremental. So,even if it is can be indicated that a certain portion of an incrementalseries of geometry elements are located within a particular tile, it maynot be possible to generate only those instances, because laterinstances may depend on iterating through earlier primitives in aprogrammatic sequence. In one implementation, unnecessarily repetitioncomputation is reduced by storing incremental geometry data in a localmemory, such as a cache. This has the advantage that, where theinstances are spread over more than one tile, predecessor geometryelements may not need to be recreated for each tile. In such animplementation, it can be defined which portions of an incrementalseries of geometry are within a particular tile or 3-D accelerationstructure element, and then those elements can be first looked forwithin a cache, before beginning a geometry process to reproduce thoseelements, which may require iterating through predecessor elements thatare not within that tile or acceleration structure element.

In an alternative embodiment, geometry modification/production may behalted after the last primitive located within a particular tile hasbeen generated. This may be determined, for example, by reading dataindicating the last primitive in the sequence located within that tile.In this embodiment, the state of a modifying unit or process may bestored, as well as the last generated modified primitive, so that themodifying or production can continue execution from where it has stoppedfor another tile. Thus, where for example the first 100 modifiedprimitives have been generated, and then the 101^(st) modified primitiveis required by a subsequent tile, the modifying unit does not have tostart re-deriving the sequence of modified primitives from thebeginning. The first modified primitive located within a particular tile(or 3-D spatial element) may be determined by reading the dataindicating the position of the first modified primitive in the sequencelocated within the tile.

In this approach, before modifications are applied to a primitiveidentified in an object list, it may be determined whether any modifiedprimitive with a corresponding identifier is stored in the cache. If so,the nearest modified primitive in the sequence to the required modifiedprimitive may be fetched, and where the state of the modifying unit hasbeen stored, the modifying unit can continue execution from thatmodified primitive until the required modified primitive is generated.In applications where the modified primitives must be generatedincrementally, the nearest modified primitive earlier in the sequencemay be required which may not necessarily be the nearest.

Once the modified instances have been re-generated, if necessary, whichones of the instances are within a particular tile may be determinedusing well known techniques, as described above. For each tile, afterdata for each of the modified primitives and non-modified primitiveslocated within that tile has been obtained, the primitives may beprocessed to render the image using well known techniques.

For example, the primitives may be passed to hidden surface removal unit70, which removes any surfaces which are not visible in the tile, andthe resulting pixel data may be passed to a texture and shading unit 80which applies pixel or texture shading before the final pixel values fordisplay are written to memory.

FIG. 2A/B depicts a joint geometry process which can be performed duringrendering that uses a hybrid of rasterization (tile-based rasterization)and ray tracing. In FIG. 2A, a geometry processing pre-pass thatproduces a stream of final geometry 82, and is used to produce (84) 3-Dobject extent data that is stored (86). 3-D object extent data can mapto nodes of an acceleration structure, be expresses identifiers fornodes of an acceleration structure, or be contained within nodes of anacceleration structure. The 3-D object extent data can indicate sourcegeometry and geometry processes to be performed on that source geometryto make final geometry and functions to identify a boundary of the finalgeometry. The stream of final geometry data is used to produce (88) 2-Dscreen space object extent data which is stored (90). Turning to FIG.2B, 3-D object extent data is used for ray tracing 9103), where rays aresorted/traversed (105) through a coarse acceleration structure. Sourcegeometry can be identified (111), where caching is used, presence offinal geometry in a cache can be checked (113). Where such finalgeometry is in a cache, then source geometry may not need to beidentified (111). If final geometry is unavailable, then that finalgeometry is recreated (115) from the source geometry. An accelerationstructure within the coarse element of the acceleration structure can becreated (117) and used for traversing (119) rays within the volume ofthat coarse acceleration structure element. Primitive testing (121) alsois performed for rays within that coarse acceleration structure element,based on the final geometry.

FIG. 2C depicts a rasterization flow where screen space tiling 123 canbe performed by beginning to process a tile (125) including accessing2-D screen space object extent data (127) (e.g., an object list) andchecking whether identified final geometry is cached (133) and to theextent not cached, providing identified source geometry and geometryprocess identification (129) to a geometry processing unit. On retrievedor recreated final geometry, HSR (visible surface identified) can beperformed. In some implementations, even though certain final geometryis not visible within a tile, some of that geometry may be cached,because it may be used for ray traversal operations. In some situations,a cache requested flag may be set for certain final geometry, whichwould indicate demand on the ray traversal side for certain portions offinal geometry (or vice versa).

FIG. 3 depicts an example implementation by which source geometry datacan be submitted through an API 180, and the source geometry data caninclude hints that indicate or which can be used to derive volumetricbounds of final geometry that will result from a particular set orelement of source geometry data. A pre-processing step can be performedwith or instead of using hints as described above. FIG. 3 thus indicatesthat although a geometry pre-pass may be performed, otherimplementations may apply hints or heuristics to obtain approximationsfor extent of final geometry from source geometry. Object extent datacan be used to identify source geometry data that will be used toproduce final geometry data needed to complete intersection testing orother operations on geometry that may be needed during ray tracing. Suchobject extent data can include a definition of a coarse accelerationstructure

Here, coarse acceleration structure can mean that rather than continuingto subdivide volumes of a given size, to create smaller groupings ofprimitives for intersection testing, the volumes are not subdivided.Therefore, the leaf nodes of a coarse acceleration structure will berelatively large and will bound a relative high number of primitives offinal geometry. In an example, a fine-grained acceleration structure maygenerally bound 5-10, 10-15, 15-20, or perhaps 20-30 or 30-50primitives, while a node of a coarse grained acceleration structure maybound one or more hundreds of primitives, or even thousands ofprimitives. These numbers can be considered in relative terms, insteadof absolute numbers or ratios.

FIG. 4 depicts a view frustrum for a pixel plane 205, and a viewfrustrum 208 for a particular tile in pixel plane 205. The view frustrumfor pixel plan 205 would be a sub-portion of an entirety of a 3-D scenein which the view frustrum would pass (even if a portion of the viewfrustrum also is outside of the 3-D scene). View frustrum 208 for aparticular tile may overlap certain elements in a coarse accelerationstructure in the scene. Overlap between these spatial entities may beused as an input in expressing object extent data for tiling and for 3-Dvolumes. For example, an object list for the tile may be expressed as aset of acceleration structure elements that enclose view frustrum 208.Each of these acceleration structure elements may have a respectiveobject list, such that the collection of these object lists forms anobject list for the tile. Some implementations may categorize elementsof final geometry based on whether they are within or within a viewfrustrum of the 2-D plane, or of a tile, or both.

FIGS. 5 and 6 depict various aspects of locating scene objects in 3-Dspace. With respect to FIG. 4, the view frustrum of FIG. 4 may belocated within the cubes depicted of FIG. 5, or partially within. Notall scene definitions are required to be cubes or other regular shapes,but for simplicity, this is depicted in the figures.

FIG. 7 depicts an approach to tuning a level of coarseness in anacceleration structure that will be used to subdivide a 3-D scene intodifferent portions, for the purpose of on-demand creation of finalgeometry of those different portions. A coarse acceleration structuremay be defined based on a criteria of how much memory can be allocatedto storing the coarse acceleration structure. This may be chosen basedon an expectation of a number of rays to be traced, where if many raysare to be traced, then a finer acceleration structure may be ofcomparatively large benefit. As explained above, rays may be collectedagainst elements of the coarse acceleration structure, and then a finergrained acceleration structure may be created before traversal of raysin that coarse acceleration structure element, or simply traversing rayswithin that structure. Some approaches may provide sorting of the rayswithin sub-portions of the coarse acceleration structure element, andcreating geometry for those sub-portions to test against an appropriatesubset of the collected rays.

FIG. 8 depicts an example process by which geometry at multipleresolutions can be produced on demand; such process also can involveproducing portions of an acceleration structure, although the example islimited to geometry. Such a process may be implemented, for example,where final geometry for a given object at a first resolution is to beprovided to a first consumer of that final geometry, while finalgeometry for that object at a second resolution is to be provided to asecond consumer of that final geometry. In a particular example, a raytracing subsystem can be provided geometry at a lower resolution for theobject than geometry that is used for a rasterization subsystem. Forexample, a total number of primitives used to define the object, whenthose primitives are used for ray tracing can be different than a totalnumber of primitives used to define that same object when rasterizingthat object.

In the example process of FIG. 8, geometry source data 350 is available,from which final geometry can be created. This geometry source data 350may comprise vertex definition data for low resolution geometry 370,supplementary vertex definition data 372, vertex connectivity data forlow resolution geometry 374 and supplementary vertex connectivity data376.

At 352, requests for final geometry within particular regions of a 3-Dspace are received from different consumers. For example, a ray tracingsubsystem and a rasterization subsystem are different consumers; thesesubsystems also each can be considered to contain multiple consumers ofgeometry. Also, particular elements of code being executed can beconsidered consumers; for example, shader modules could make geometryrequests. Regions of 3-D space can be identified in different ways. Forexample, a rasterization subsystem may identify a tile within an imageto be rendered, and that tile can be used to index a mapping of regionsof 3-D space within a view frustrum of that tile. A ray tracingsubsystem may identify an element of an acceleration structure.Consumers may identify a geometry object or list of objects for whichfinal geometry is to be produced. Thus, it would be understood thatimplementations may vary in how consumers of geometry can indicate whichgeometry is being requested (and the same for acceleration structureelements).

At 354, these requests are categorized, such as according to whethereach requests high or low resolution geometry. Although this exampleconcerns two available geometry resolutions, more resolutions may beprovided, or there may be a programmatically configurable geometrygeneration that can create final geometry according to a target that isnot directly expressed in terms of resolution or primitive count, forexample. In one approach, at 356, a selected portion of vertexconnectivity data is applied to an appropriate portion of vertex datafrom geometry source data 350, for each of the consumers, for each ofthe regions of 3-D space in which geometry was requested. The finalizedgeometry is outputted at 358.

FIG. 9 depicts an example memory map 382 of how vertex data and vertexconnectivity data can be arranged in memory. In FIG. 9, vertexdefinition data for low-resolution geometry 388 can be stored separatelyfrom supplemental vertex definition data 390, and vertex connectivitydata for low resolution geometry 392 can be stored separately fromvertex connectivity data for high-resolution geometry 394. In order tocreate geometry at a particular resolution, the base line low resolutiongeometry may always be accessed, and then selections from supplementalvertex definition data can be accessed, along with appropriate portionsof vertex connectivity data.

Other approaches laying out geometry data for storage in memory arepossible. For example, vertex data pertaining to specific regions of 3-Dspace can be stored together; for example, low resolution andsupplemental vertex definition data for a particular region of 3-D spacecan be stored together. This approach provides that low resolution andsupplemental vertex definition data would then be interleaved. Anobject-by-object aggregation of low resolution and supplemental vertexdefinition data also can be provided. These options can both be used insome approaches.

The example of FIG. 8 relates primarily to generating geometry usingselections from sets of primitive data. However, in otherimplementations, higher resolution geometry can be generated from lowerresolution geometry by procedural modification. Such implementations canuse higher order surface definition data (rather than primitive data),and that higher order surface definition data can be processed accordingto one or more geometry processes in order to produce geometry at adesired resolution. Although these examples primarily treat differentresolution geometry, implementations of on demand geometry processingalso can produce different kinds of final geometry for differentconsumers. Also, some implementations may produce and/or output adifferent subset of primitives, even at a given resolution. For example,geometry production that is intended for consumption by a rasterizationsubsystem may clip geometry to a view frustrum of an image, or of a tilewithin the image, and/or cull backfacing primitives. However, backfaceculling of primitives of an object would not be performed for a raytracing subsystem.

FIG. 10 depicts an example process of controlling scheduling and/orcaching of acceleration structure elements and geometry data. In asituation where resources are unconstrained, scheduling of geometryproduction may simply provide in order processing of requests asreceived. However, such an approach leaves optimization available, asexplained below. At 410, requests for geometry within a particular 3-Dregion (which can come from different consumers) are received. At 412,these requests are collected into groups according to 3-D region. At414, geometry and/or acceleration structure element production for thesegroups is scheduled according to scheduling criteria. Thus, in a firstimplementation, requests are not processed in order, but are deferredwithin a scheduling window in order to identify requests that pertain tothe same region of 3-D space (or to the same object, for example). Suchscheduling 414 also can use inputs descriptive of prediction(s) ofdemand for particular geometry or acceleration structure elements.

Scheduling can involve determining how much computation resource can beused for geometry production, and a number of groups concurrentlyprocessed can be selected accordingly. Priority can be given to 3-Dregions of space having more requests. A request from a rasterizationsubsystem can be weighted more highly than a request from a ray tracingsubsystem. Some systems may have multiple frames in flight, and requestspertaining to earlier frames can be prioritized over requests from laterframes. Scheduling also can involve comparing an expected amount ofgeometry and/or acceleration structure elements that would be producedto complete a given request, and determining whether sufficient memoryis available. Still further scheduling criteria can include determiningwhether source geometry is available in a cache for some portionrequests, and prioritizing those requests. Conversely, requests can beculled if final geometry or acceleration structure elements are presentin a cache (or otherwise directly serviced from the cache); for example,a request can simply be a request for final geometry—not necessarily arequest to produce such geometry. A geometry production process canreturn the geometry requested (or provide a references or set ofreferences to memory storing such geometry).

Aside from servicing requests from existing geometry data, at 416,requested geometry and/or acceleration structure elements are produced.During such production, at 418, metadata concerning such production canbe collected. Such metadata can include a size of the data produced, amemory access pattern for source geometry, an amount of computationrequired to produce the geometry, and so on. This metadata can be usedin scheduling at 414, as well as determining caching of such data(described below). At 419, consumers of produced data can use such dataas needed. Such usage may occur over a period of time and may occurconcurrently with generation of other data. Action 419 is includedprimarily to address applicability of actions 420-426 that follow.

At 420, caching/cacheability characteristics for geometry and/oracceleration data produced are determined. Such determination can useindicia 424 of demand for such geometry and/or acceleration structureelements. Such determination also can use metadata collected at 418. Forexample, geometry that required a great deal of computation to beperformed may be ranked more highly for caching than other geometry.These caching/cacheability characteristics may be effected by directinga cache coherency manager or cache replacement manager to expect aparticular number of reads for a given set of data, and then to allowthe data to be evicted.

At 426, scheduling hints directed to execution modules can be generated.For example, geometry processing may occur asynchronously fromconsumption of the geometry. Although it may be expected that a givenconsumer may be alerted to the availability of geometry that isresponsive to a given request, as a basic hint, hints also may alert theconsumer that such geometry has been given a certain caching priority.For example, if certain data has been given a low caching priority, thenit is more likely that the data may be overwritten or evicted (spilled)to another layer of the cache hierarchy or to main memory. As such, theconsumer may elect to prioritize usage of that data. Someimplementations may use the combination of caching and scheduling hintsto effect a relative order of consumption of the geometry data. Forexample, some produced geometry data may be initially cached and somestored in main memory, and scheduling hints can identify which data iswhere. Consumers having data stored in the cache would be expected touse that data within a scheduling window, as it will become more likelyto be overwritten as time progresses, or may even be explicitlyoverwritten by other geometry data, or spilled to main memory.

FIG. 11 depicts an example of data 453 that can be stored foracceleration structure elements, which may be used in schedulingproduction of geometry or usage of produced geometry within suchelements. For example, a number of ray groups that need to traverse thatelement. Hints concerning what a fine grained acceleration structurelocated within that coarse element can be provided. Such hints caninclude how many elements are within the coarse element. Hintsconcerning primitive characteristics can be provided (e.g., a number ofprimitives.) Complexity hints can be provided; such hints relate to anamount of resource consumption is required to produce accelerationstructure elements and/or final geometry within that coarse grainedelement.

FIG. 12 depicts an example 460 of tracking rays according to traversalstatus. For example, rays can be concurrently traversed in multipledifferent parts of an acceleration structure. Different computationarchitectures can implement ray traversal differently. For example, someimplementations may create a thread for each ray and that thread isresponsible for fully traversing the ray. Then, example 460 can trackwhich acceleration structure element would be next visited by each ray.Other implementations can maintain a set of threads (or other functionalelements) that are for traversing varying rays and/or for testingdifferent sets of rays for intersection with different sets ofprimitives, for example.

FIG. 13 depicts an example of modules that can be involved in suchon-demand acceleration structure/geometry creation and consumption. Forexample, geometry processes 462, and acceleration structure processes464 are responsible for creating final geometry and accelerationstructures respectively. Ray tracing processes 466 and geometry tilingprocesses 468 are example consumers of such geometry. These processescan communicate with memory arbitration/control 470, which isresponsible for managing cache hierarchy 476 (and for example, mainmemory 478); this element can use the caching hints described above.Processor scheduling 474 is responsible for coarse-grained scheduling orallocation of different tasks to different computation resources.Processor scheduling 474 can intake and use the processor schedulinghints described above. Elements 470 and 474 can coordinate, in order toimplement staged transfer and consumption of produced data.

FIG. 14 depicts aspects of an example execution unit that can implementthe elements depicted in FIG. 13. A coarse scheduler 502 allocates tasksacross a set of vectorized execution units 504, each of which caninclude one instruction fetch/decode unit and a set of processingelements driven by that fetch/decode unit. Coarse scheduler 502 canexecute on a vectorized execution unit or on a management processor (notdepicted). These vectorized execution units 504-506 communicate with acache hierarchy 510. Cache hierarchy 510 may provide a set of privatememories (e.g., an L1 cache) for each execution unit, as well as otherlevels of cache hierarchy. Cache hierarchy 510 may communicate with amain memory 512. A cache coherency controller 515 may consume cachinghints and control which data is evicted from cache hierarchy 510 andwhich data is pre-fetched. Fixed and/or limited programmabilityaccelerators 514 may be implemented for some kinds of processing. Forexample, a fixed-function ray/primitive intersection test element may beprovided.

FIG. 15 depicts an example of a vectorized execution unit. Such exampleincludes an input queue 524 for receiving definitions of tasks, a frontend, which can maintain data that tracks various threads in flight onthe unit, and can decode instructions. A fine grained scheduler 522 candetermine on a clock cycle by clock cycle basis which thread will bepermitted to execute instruction(s) on a set of SIMD execution units526-527. Each of these units can access a register file (not separatelydepicted). Such register file can be implemented as an L1 cache, orpartially as a cache and partially as a register file (e.g., someportion of it can be managed by cache coherency control 515 and someportion not).

These disclosures can factor into a throughput oriented general purposecomputation system, where on demand geometry processing can be scheduledalong with other computation with a scheduling process that groupsworkloads according to scheduling keys. These scheduling keys canrepresent a variety of specific task-based information. For example, ascheduling key can refer to an element of a coarse-grained accelerationstructure, and when referenced by a geometry creation process, can bescheduled as a request for on demand geometry creation. Other exampletask-oriented processes can include more granular tasks, such as testinga ray for intersection with a primitive, or testing a ray forintersection with an acceleration structure element. These schedulingaspects can be applied to other computation where there is a producer ofa data element that is consumed by another computation unit orprocessing element, such as video decoders and pattern recognitionkernels, compressors, and so on. Processes can be treated by ascheduling process according to whether they are jitter or latencytolerant. For example, some processes, such as a microphone inputprocessor is not jitter tolerant, and therefore, a scheduling processwould not schedule microphone input processing as a peer of raytraversal tasks.

In the context of graphics processing, a frame shader can produce raysto be traversed by a consumer ray traversal unit. A shader can producedata to be consumed by another shader. For example, a shader may wantanother shader(s) to execute for a reason like handling the exit from amaterial that is applying distance-dependent attenuation (e.g. murkywater) where the other material (shader) might be specified or affectedby a value attached to the ray. As such, an intersection may trigger twodifferent shaders to execute, which can execute serially or in parallel(serially where one shader may provide inputs to the next shader).Closures, where a shader outputs an intermediate result that is an inputto a closure also is a model that can be scheduled according to thesedisclosures.

More specifically relating to geometry processing, a vertex shader orgeometry shader (outputting polygons/geometric primitives) may have itsoutput sent towards or enqueued to a hierarchy building process.Contribution values may be produced by various producers, and can passthrough a queue to a kernel that does the read-modify-write of the pixelvalues in a cache friendly way.

Producers can enqueue outputs in a queue to be read by one or moreconsumers; collections can be formed based on enqueued outputs. Forexample, in ray tracing, a ray can be amended to one or more collectionsfor the respective child elements, which will be read by one or moretest units. In some cases, an order establishment module may set anorder for a plurality of peer collections (e.g., a set of elements thatall are to be tested with respect to one or more rays). For example, anelement can be prioritized for testing over other elements if it has alower average distance to different rays to be tested with respect toall those elements. A random or representative ray can be selected fordistance testing.

Rays can be emitted from surfaces that were determined to be visible bya rasterization process. However, rays also can be tested forintersection against low resolution (e.g., low polygon count) models ofobjects located in a given 3-D scene, while rasterization can use higherresolution models of the same objects. Thus, it should be understoodthat tracing rays from a visible surface identified by a rasterizationprocess does not preclude determining an origin and/or direction for agiven ray based on geometry data defined for use in the ray tracingcontext. For example, a location of a surface where a ray would beemitted for the low versus the high polygon counts may differ; however,the scope of the claims include defining rays based on either modelinvolved, or based on an absolute position in 3-D space, for example.

The order of activities depicted in the diagrams is not by way oflimitation that such activities must be, or are preferred to beperformed in that order. Additionally, there may be situations where notall depicted activities are performed for a given synchronizationoperation. For example, some data or table organization or formattingmay already have been performed, and so, such activities would not needto be performed again.

As would be apparent from the disclosure, some of the components andfunctionality disclosed may be implemented in hardware, software,firmware, or any combination thereof. If implemented in firmware and/orsoftware, the functions may be stored as one or more instructions orcode on a computer-readable medium, in one example, the media isnon-transitory. Examples include a computer-readable medium encoded witha data structure and a computer-readable medium encoded with a computerprogram. Machine-readable media includes non-transitory machine readablemedia. Other kinds of media include transmission media. A non-transitorymedium may be any tangible medium that can be accessed by a machine. Byway of example, and not limitation, such computer-readable media cancomprise RAM, ROM, EEPROM, CD-ROM or other optical disk storage,magnetic disk storage or other magnetic storage devices, or any othermedium that can be used to store desired program code in the form ofinstructions or data structures and that can be accessed by a machine.

Those of skill will also appreciate that the various illustrativelogical blocks, modules, circuits, and algorithm steps described inconnection with the embodiments disclosed herein may be implemented aselectronic hardware, computer software in a computer-readable medium, orcombinations of both. To clearly illustrate this interchangeability ofhardware and software, various illustrative components, blocks, modules,circuits, and steps have been described above generally in terms oftheir functionality. Whether such functionality is implemented ashardware or software depends upon the particular application and designconstraints imposed on the overall system. Skilled artisans mayimplement the described functionality in varying ways for eachparticular application, but such implementation decisions should not beinterpreted as causing a departure from the scope of the presentinvention.

The description of the aspects and features is provided to enable anyperson skilled in the art to make and use the systems, apparatuses andperform the methods disclosed. Various modifications will be readilyapparent to those skilled in the art, and the principles described inthis document may be applied to other aspects without departing from thespirit or scope of the disclosure. Thus, the description is not intendedto limit the claims. Rather, the claims are to be accorded a scopeconsistent with the principles and novel features disclosed herein.

The drawings include relative arrangements of structure and ordering ofprocess components, solely as an aid in understanding the description.These relative arrangements and numbering is not an implicit disclosureof any specific limitation on ordering or arrangement of elements andsteps in the claims. Process limitations may be interchangedsequentially without departing from the scope of the disclosure, andmeans-plus-function clauses in the claims are intended to cover thestructures described as performing the recited function that include notonly structural equivalents, but also equivalent structures.

Although a variety of examples and other information was used to explainaspects within the scope of the appended claims, no limitation of theclaims should be implied based on particular features or arrangements insuch examples, as one of ordinary skill would be able to use theseexamples to derive a wide variety of implementations. Further andalthough some subject matter may have been described in languagespecific to examples of structural features and/or method steps, it isto be understood that the subject matter defined in the appended claimsis not necessarily limited to these described features or acts. Forexample, such functionality can be distributed differently or performedin components other than, additional to, or less than, those identifiedherein. Rather, the described features and steps are disclosed asexamples of components of systems and methods within the scope of theappended claims.

The invention claimed is:
 1. A machine-implemented method for use in 3-Drendering, comprising: accessing, by a processor, geometry datadescribing geometry located in a 3-D scene, from which a rendering is tobe produced, the geometry data describing: geometry control points thatdefine one or more surfaces of the geometry located in the 3-D scene,and procedural modifications that can be performed on the geometrycontrol points to produce final geometry on which the rendering will bebased; and producing, by a processor, using the final geometry, geometryextents data that establishes an association between a volume defined inthe 3-D scene and geometry control points that would, after proceduralmodification, produce final geometry within the defined volume on whichrendering will be based; storing the geometry extents data; andrendering a scene in said defined volume using final geometry producedby said stored geometry extents data.
 2. The machine-implemented methodfor use in 3-D rendering of claim 1, further comprising defining rays tobe traced in the 3-D scene, by identifying a volume in the 3-D space inwhich a subset of the rays is to be tested for intersection, using thegeometry extents data to identify geometry control points that producefinal geometry in the identified volume in the 3-D space, then executingany procedural modifications for those identified geometry controlpoints to produce final geometry in the identified volume, and thentesting final geometry for intersection with the subset of the rays. 3.The machine-implemented method for use in 3-D rendering of claim 1,further comprising defining the volumes in 3-D space as comprisingfrustra for each screen space tile of a plurality of tiles, eachcomprising a plurality of pixels and that collectively define a 2-Dimage to be rendered.
 4. The machine-implemented method for use in 3-Drendering of claim 1, further comprising producing an accelerationstructure comprising elements bounding respective portions of the 3-Dscene, and using the acceleration structure to identify respectivesubsets of the final geometry to be tested for intersection withdifferent rays.
 5. The machine-implemented method for use in 3-Drendering of claim 1, further comprising using hint data to define thevolumes in the 3-D scene that are referenced in the geometry extentdata.
 6. The machine-implemented method for use in 3-D rendering ofclaim 1, further comprising associating procedural modifications withgeometry extents data that are required to produce final geometry withina volume of the 3-D scene to which the geometry extents data pertains.7. The machine-implemented method for use in 3-D rendering of claim 6,further comprising making a rendering using both a rasterizationsubsystem and a ray tracing subsystem that each make requests forportions of final geometry, and responsive to the requests, producingthe final geometry by performing the procedural modifications associatedwith the geometry extents data associated with volumes of the 3-D scenebounding the requested portions of final geometry.
 8. Themachine-implemented method for use in 3-D rendering of claim 7, whereinthe method further comprises producing final geometry having a level ofdetail dependent on whether to the request originated from the raytracing subsystem or the rasterization subsystem.
 9. Themachine-implemented method for use in 3-D rendering of claim 7, whereinthe method further comprises producing both a finalized accelerationstructure within a portion of the 3-D scene and final geometry withinthat portion of the 3-D, responsive to a request from the ray tracingsubsystem.
 10. The machine-implemented method for use in 3-D renderingof claim 1, further comprising producing a coarse acceleration structurewith leaf elements and using leaf elements of the coarse accelerationstructure as the geometry extents data.
 11. The machine-implementedmethod for use in 3-D rendering of claim 10, further comprisingcollecting rays to be traced against elements of the coarse accelerationstructure and traversing rays collected against a particular element ofthe coarse acceleration structure by dynamically producing a finalizedacceleration structure within that particular element of the coarseacceleration structure prior to scheduling traversal operations for thecollected rays.
 12. The machine-implemented method for use in 3-Drendering of claim 11, further comprising producing final geometrywithin portions of the finalized acceleration structure responsive to ascheduler indication.
 13. The machine-implemented method for use in 3-Drendering of claim 1, wherein the accessing and producing are performedin a pre-pass over source geometry data, the source geometry datacomprising vertex data and two or more sets of vertex connectivity data.14. The machine-implemented method for use in 3-D rendering of claim 1,wherein the procedural modifications that can be performed on thegeometry control points comprise procedural modifications to be used forproducing finalized geometry for ray tracing and proceduralmodifications to be used for producing finalized geometry forrasterization.
 15. The machine-implemented method for use in 3-Drendering of claim 1, wherein the producing of the geometry extents datacomprises producing a hint indicating an amount of geometry expansion tobe expected when producing final geometry for the volume defined in the3-D scene that is associated with that portion of geometry extents data.16. The machine-implemented method for use in 3-D rendering of claim 1,wherein accessing comprises accessing a hint that is associated with acontrol point, which indicates a bound on an amount of geometry that mayresult when performing procedural modification using that control point,to produce final geometry.
 17. The machine-implemented method for use in3-D rendering as claimed in claim 1, further comprising: identifying avolume in the 3-D scene; creating on demand final geometry in theidentified volume by: selecting geometry control points using storedgeometry extents data associated with the identified volume; andperforming procedural modification on the selected geometry controlpoints to produce the final geometry.
 18. A graphics rendering systemcomprising: a geometry processing element configured to: access geometrydata describing geometry located in a 3-D scene, from which a renderingis to be produced, the geometry data describing geometry control pointsthat define one or more surfaces of the geometry located in the 3-Dscene and procedural modifications that can be performed on the geometrycontrol points to produce final geometry on which the rendering will bebased, and produce, using the final geometry, geometry extents data thatestablishes an association between a volume defined in the 3-D scene anda selection of the geometry control points that, after proceduralmodification, produce final geometry that respectively is within thatvolume, and store the geometry extents data; and a rendering subsystemconfigured to generate requests for finalized geometry within portionsof the 3-D scene, the requests to be serviced by the geometry processingelement, and to use finalized geometry returned in response to therequests to produce a rendering from the 3-D scene.
 19. The graphicsrendering system of claim 18, wherein the rendering subsystem comprisesa ray tracing subsystem for tracing rays in the 3-D scene, the raytracing subsystem configured to identify a volume in the 3-D scene inwhich a subset of rays is to be tested for intersection, and arasterization subsystem.
 20. The graphics rendering system of claim 18,wherein the finalized geometry is produced by the geometry processingelement for each respective portion of the 3-D scene by: selectinggeometry control points using stored geometry extents data associatedwith an identified volume of the respective portion of the 3-D scene;and performing procedural modification on the selected geometry controlpoints to produce the final geometry in the respective portion of the3-D scene for rendering.